Chapter 14: Breathing and Exchange of Gases Application Questions | biology Class 11 CBSE

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Chapter 14: Breathing and Exchange of Gases Application Questions | biology Class 11 CBSE | ByteNotes.in

Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 1

Applied Concept

A patient in hospital is put on a mechanical ventilator that forces air into the lungs and withdraws it. With reference to normal breathing mechanism, explain why this works and what pressure changes the ventilator is mimicking.

Normal breathing works by creating a pressure gradient between the lungs and atmosphere; inspiration occurs when intra-pulmonary pressure drops below atmospheric pressure and expiration when it rises above.
The ventilator mimics inspiration by forcing air in under positive pressure, inflating the lungs, and mimics expiration by allowing or actively withdrawing air — recreating the pressure gradient artificially.
In a patient who cannot use their diaphragm or intercostal muscles (e.g., due to paralysis), the ventilator substitutes for these muscles in generating the necessary thoracic volume and pressure changes.
The principle exploited is the same: any mechanism that lowers intra-pulmonary pressure relative to atmosphere moves air into the lungs, and any mechanism that raises it above atmosphere expels air.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 2

Applied Concept

A mountaineer climbing to high altitude experiences difficulty breathing and reduced oxygen supply to tissues. With reference to partial pressure gradients, explain the physiological basis of this problem.

At high altitudes, atmospheric pressure decreases, so the partial pressure of O2 in atmospheric air falls well below the normal 159 mm Hg.
A reduced pO2 in inhaled air means the pO2 in the alveoli also decreases, narrowing or reversing the concentration gradient between alveolar air and deoxygenated blood (normally pO2 = 104 in alveoli vs 40 in deoxygenated blood).
With a reduced alveolar pO2, less O2 diffuses into the blood, so haemoglobin is less saturated with O2, and less O2 is delivered to tissues.
The body responds by increasing breathing rate (hyperventilation) as the respiratory rhythm centre is stimulated, but at extreme altitudes this compensation is insufficient to maintain normal tissue oxygenation.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 3

Applied Concept

During intense exercise, both breathing rate and depth increase dramatically. With reference to the regulation of respiration, explain why this happens.

During intense exercise, cells undergo rapid catabolism, producing large amounts of CO2 and H+ ions, which raise blood pCO2 and lower pH.
The chemosensitive area adjacent to the respiratory rhythm centre in the medulla detects the increase in CO2 and H+ and activates the rhythm centre.
The rhythm centre increases both the rate and depth of breathing to expel excess CO2 and bring in more O2; additional abdominal muscles are recruited for forced expiration.
Peripheral receptors in the aortic arch and carotid artery also detect elevated CO2 and H+ and relay signals to the rhythm centre — the combined effect is a rapid increase in ventilation that matches the heightened metabolic demand.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 4

Applied Concept

A heavy smoker visits a pulmonologist complaining of chronic shortness of breath and inability to exercise. Tests show a greatly increased residual volume. Which disorder does this suggest, and explain the mechanism of the lung damage.

The chronic shortness of breath combined with increased residual volume in a heavy smoker strongly suggests emphysema.
In emphysema, alveolar walls are damaged (and destroyed); the chapter identifies cigarette smoking as one of the major causes of this chronic disorder.
Destruction of alveolar walls reduces the total respiratory surface area available for gas exchange, severely impairing O2 uptake and CO2 elimination.
With alveolar walls gone, smaller alveoli merge into larger, less elastic spaces — air becomes trapped (increasing RV), and the loss of elasticity makes expiration more difficult, causing the breathlessness reported by the patient.

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Application Question

Easy difficulty • Concept in a practical situation

Easy

Question 5

Applied Concept

A student accidentally inhales a small piece of food. Explain, with reference to the structural features of the upper respiratory tract, what normally prevents this and why the student began choking.

The pharynx serves as a common passage for both food and air, making the entry of food into the larynx a risk every time a person swallows.
Normally, the epiglottis — a thin elastic cartilaginous flap at the larynx — covers the glottis (opening into the trachea) during swallowing, preventing food from entering the respiratory tract.
If the student was eating and talking or laughing simultaneously, the epiglottis may not have covered the glottis in time, allowing a food particle to pass into the larynx.
The food particle entering the larynx and trachea triggers a coughing reflex (choking) as the body attempts to expel the foreign object and clear the airway — a critical protective mechanism.

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Application Question

Hard difficulty • Concept in a practical situation

Hard

Question 6

Applied Concept

In a clinical pulmonary function test, a patient's Vital Capacity is found to be significantly lower than normal. Using respiratory volume formulas, explain what this implies and how it could relate to lung disease.

Vital Capacity (VC) = ERV + TV + IRV; a reduced VC means the patient cannot exchange as much air as a healthy person, even with maximum effort.
Reduced VC could result from decreased IRV (inability to fully expand the lungs), decreased ERV (inability to fully exhale), or both — indicating restricted lung expansion or airway obstruction.
In restrictive conditions (e.g., fibrosis), lung compliance decreases and VC falls because the lungs cannot fully expand; in obstructive conditions (e.g., emphysema), air trapping increases RV while reducing ERV and thus VC.
The clinician would use a spirometer to measure these volumes precisely, and by combining VC with RV to determine TLC, and analysing the pattern of volume reduction, the type and severity of lung disease can be diagnosed.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 7

Applied Concept

Explain why workers in stone-crushing factories are at high risk of serious lung diseases, and suggest why wearing masks is the primary recommended preventive measure.

Stone-crushing and grinding industries produce enormous quantities of fine dust particles that are inhaled continuously during work; the body's normal defence mechanisms cannot clear this excessive load of particles.
Chronic dust inhalation leads to persistent inflammation of the respiratory tract; over time this progresses to fibrosis — proliferation of fibrous tissue — causing serious, progressive lung damage.
Fibrosis reduces lung compliance and the effective respiratory surface, impairing gas exchange and causing occupational respiratory disorders.
Wearing protective masks physically blocks the inhalation of dust particles at the source — since the damage is caused by particle inhalation and not by a toxin or organism, preventing particle entry is the most direct and effective preventive measure.

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Application Question

Hard difficulty • Concept in a practical situation

Hard

Question 8

Applied Concept

With reference to the oxygen dissociation curve, explain why a patient with severe anaemia (reduced haemoglobin) suffers from oxygen deficiency at tissues even though their pO2 may be normal.

The oxygen dissociation curve shows the relationship between pO2 and percentage saturation of haemoglobin with O2; a normal pO2 at the alveoli means the available haemoglobin will be fully saturated.
However, in severe anaemia, the total quantity of haemoglobin in the blood is greatly reduced; since 97% of O2 is transported bound to haemoglobin, less total O2 is carried even if each haemoglobin molecule is 100% saturated.
When oxygenated blood reaches tissues, even full dissociation of the reduced amount of haemoglobin delivers insufficient O2 to meet cellular metabolic demands.
Thus, the problem is not impaired O2 loading (saturation is fine) but reduced O2-carrying capacity — the chapter notes every 100 mL of oxygenated blood normally delivers about 5 mL O2, but anaemia reduces this dramatically.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 9

Applied Concept

An asthma patient uses an inhaler during an attack. With reference to the nature of asthma, explain why inhaling a bronchodilator drug provides rapid relief.

Asthma is described as a difficulty in breathing causing wheezing due to inflammation of bronchi and bronchioles — the inflamed airways become narrowed, restricting airflow.
A bronchodilator drug relaxes the smooth muscle of the bronchi and bronchioles, widening the narrowed airways and reducing airway resistance.
Inhaling the drug delivers it directly to the site of inflammation (bronchi and bronchioles) and acts rapidly — bypassing systemic circulation — making it far more effective and faster than an oral route.
Once the airway diameter increases, the pressure gradient needed for airflow is restored, intra-pulmonary pressure equilibrates more easily with atmospheric pressure, and normal inspiration and expiration resume.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 10

Applied Concept

Explain why the pCO2 in deoxygenated blood (45 mm Hg) is higher than in alveolar air (40 mm Hg), and how this gradient drives CO2 out of the blood at the lung surface.

At the tissue level, cells continuously produce CO2 through catabolism; this CO2 diffuses into the blood (where it is transported as bicarbonate, carbamino-haemoglobin, and dissolved), raising pCO2 in deoxygenated blood to 45 mm Hg.
When this deoxygenated blood reaches the pulmonary capillaries surrounding the alveoli, the pCO2 in alveolar air is 40 mm Hg — lower than in the blood.
This 5 mm Hg partial pressure gradient drives CO2 to diffuse from blood across the thin diffusion membrane into the alveolar air; CO2's solubility (20–25x higher than O2) ensures efficient diffusion despite this small gradient.
At the alveolar site, low pCO2 also drives the carbonic anhydrase reaction in reverse — bicarbonate and H+ are converted back to CO2 + H2O, releasing more CO2 into alveolar air for exhalation.

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Chapter 14: Breathing and Exchange of Gases | Application Questions

A patient in hospital is put on a mechanical ventilator that forces air into the lungs and withdraws it. With reference to normal breathing mechanism, explain why this works and what pressure changes the ventilator is mimicking.

A mountaineer climbing to high altitude experiences difficulty breathing and reduced oxygen supply to tissues. With reference to partial pressure gradients, explain the physiological basis of this problem.

During intense exercise, both breathing rate and depth increase dramatically. With reference to the regulation of respiration, explain why this happens.

A heavy smoker visits a pulmonologist complaining of chronic shortness of breath and inability to exercise. Tests show a greatly increased residual volume. Which disorder does this suggest, and explain the mechanism of the lung damage.

A student accidentally inhales a small piece of food. Explain, with reference to the structural features of the upper respiratory tract, what normally prevents this and why the student began choking.

In a clinical pulmonary function test, a patient's Vital Capacity is found to be significantly lower than normal. Using respiratory volume formulas, explain what this implies and how it could relate to lung disease.

Explain why workers in stone-crushing factories are at high risk of serious lung diseases, and suggest why wearing masks is the primary recommended preventive measure.

With reference to the oxygen dissociation curve, explain why a patient with severe anaemia (reduced haemoglobin) suffers from oxygen deficiency at tissues even though their pO2 may be normal.

An asthma patient uses an inhaler during an attack. With reference to the nature of asthma, explain why inhaling a bronchodilator drug provides rapid relief.

Explain why the pCO2 in deoxygenated blood (45 mm Hg) is higher than in alveolar air (40 mm Hg), and how this gradient drives CO2 out of the blood at the lung surface.

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